Austria-Hungary declares war on Serbia, 28 July 1914
It’s one month to the day after Serbian nationalists killed Archduke Franz Ferdinand and the Duchess of Hohenberg that Austria-Hungary declares war on Serbia. The action effectively begins the irreversible steps that lead to the Great War, and the destruction of Western Europe.
After a month, Austria-Hungary had determined that a proper measured response to the assassination of their royals was possible military invasion of Serbia. It’s with unconditional support from Germany—the so-called Blank Check assurance on 5 July—that allows Austria-Hungary to present Serbia with an ultimatum on 23 July 1914: the Empire demands a list of things, but among them that all anti-Austrian propaganda within Serbia to be suppressed, and that Austria-Hungary be given full reign of conducting their own investigation into the Archduke’s murder. Serbia grudgingly accepted the terms, only to have the Austrian government break diplomatic relations.
In an effort to stop the building conflict from bursting, the British Foreign Office lobbied in partnership with French officials in Berlin, Paris and Rome to bring the countries to a table. They fail; the German government wants no part in peace. They advise Vienna to go ahead, and when Austria-Hungary declares war on Serbia on 28 July 1914, Russia (the protector of the Balkans) fully mobilizes its military.
That night, Austrian artillery initiate bombardment of Belgrade.
By 1 August 1914, Germany has declared war on Russia.
By 3 August 1914, Germany has declared war on France.
The Great War has begun.